1. Field of the Invention
The present invention relates to the field of data transfer through an Ethernet network. More particularly, the present invention relates to a system and method for real-time modification of Inter Frame Spacing associated with the Ethernet network to improve its overall performance.
2. Description of Art Related to the Invention
With the continual emergence of smaller, faster and more powerful computers, many businesses have implemented or are in the process of implementing decentralized networks such as local area networks ("LANs"). A LAN is a high-speed communications network which electrically connects a collection of stations (e.g., computers, servers, plotters or any other electronic network connective device) together. As a result, each user has control over his or her own station and has access to other stations coupled to the LAN. One well-known type of LAN is commonly referred to as an "Ethernet network".
Defined by IEEE Standard 802.3 (IEEE, 1993), the Ethernet network is a non-priority based network which possesses a bus supporting a limited bandwidth currently 10 million bits per second ("Mbps") and 100 Mbps. The IEEE 802.3 standard currently uses the Carrier Sense Multiple Access and Collision Detection ("CSMA/CD") access method which attempts to prevent collisions by using a carrier signal to indicate when a frame of data (i.e., "data frame") is being transmitted by a station. A "data frame" is a sequence of data bits of a preselected length.
If the carrier signal is asserted, a station requesting access to the Ethernet network monitors the carrier signal until it goes inactive and thereafter, waits at least a minimum Inter Frame Spacing ("IFS") delay which is 9.6 microseconds (".mu.s") for a 10 Mbps Ethernet network or 960 nanoseconds ("ns") for a 100 Mbps Ethernet before transmitting its data frame. This behavior is observed even when only one station is transmitting by requiring the station to wait until the IFS delay has expired before it can transmit another data frame. Therefore, the fastest possible data transmission, called a "Back-to-Back (BtB) transmit", occurs when successive transmits are separated by only an IFS delay.
A collision occurs when one or more stations attempt to transmit a data frame before a prior data transmission of other station is complete. For example, suppose two stations are connected to 10 Mbps Ethernet network having a propagation delay between stations greater than 9.6 .mu.s. When the first station begins to transmit a data frame, the second station will receive an active carrier signal only after the propagation delay. However, if the second station is monitoring the carrier signal, it will start to transmit a data frame after 9.6 .mu.s (i.e., a minimum IFS delay) which may inadvertently cause a collision to occur.
According to the IEEE 802.3, all stations whose data frames have collided must discontinue transmissions and wait a random number of "slot times" before attempting to re-transmit its data frame. A "slot time" is a maximum propagation delay for a signal to travel from a first station (e.g., a computer) of the Ethernet network to a second station (e.g., a server) and back to the first station via the bus of a maximum length supported by the Ethernet network. The "slot time" of the 10 Mbps Ethernet network is equal to 51.2 .mu.s. Stations in contention that have chosen the same "random" number will experience another collision caused by re-transmission of its frame and perhaps future frame collisions. Moreover, it is contemplated that other stations, not originally in contention, may also cause collisions by attempting to transmit data flames after appropriate IFS delay.
Otherwise, if operating contrary to the guidance of IEEE 802.3, the Ethernet network may experience an unacceptably high data collision rate which reduces available bandwidth of the Ethernet network and leads to less than optimal performance. Likewise, increasing the IFS for a given Ethernet network configuration may temporarily reduce the number of data collisions experienced by the Ethernet network, however, it is contemplated that the IFS could be excessive in the event that traffic on the Ethernet network significantly decreases. This would also prevent the Ethernet network from achieving its optimal performance level.
Therefore, it would be advantageous to control the time value of IFS associated with the Ethernet network based on a number of factors such as network traffic and topology. It would be required, however, for such control to be "on the fly" or in real-time to support real-time data transmissions.